You're supposed to build ever widening highways to an ever expanding web of roads to distant suburbs that are too low density to be effectively serviced by mass transsit, so when the roads get clogged you build more roads, and then widen them, and then build more until finally you've got too many choke points to accommodate any further growth and end up with a city characterized by long, miserable and expensive driving commutes that is completely unsuitable for adapting to mass transit.